Central Flying Academy Power-On Stalls
Power-On Stalls Happen Where You Least Expect Them
Ask someone where they think a power-on stall is likely to happen, and they usually say "takeoff". But there are relatively few power-on stall accidents during takeoff, mostly because pilots are focused on one thing: takeoff.
Power-on stalls happen more often during go-around, and there are three reasons why. During a go-around distractions are high, the aircraft is trimmed for landing, and retracting flaps causes a pitch change.
Go Around: Ripe For Distraction
Pilots typically go-around for two reasons:
- There's traffic preventing them from landing.
- The aircraft isn't stabilized for landing.
Both reasons can cause problems.
If you have to go-around because of traffic on the runway or near you in the pattern, it also means you're going to be spending time communicating with that airplane, or ATC, to make sure there's blue sky between everyone. And when you're talking on the radio and low to the ground, you have less time to focus on things like airspeed and pitch attitude.
If you're going around because you're unstabilized or you had a bad touchdown, distraction sets in (and frustration too). Are you thinking about how you screwed up your approach-to-landing, or are you thinking about what airspeed you're pitching for on go-around?
Sometimes, it can be a combination of distraction and communication, like this accident:
On the student pilot's second solo landing the airplane landed hard and bounced twice. The flight instructor, standing on the side of the runway, radioed instructions to "go-around". The student pilot then applied full power, applied right rudder and retracted one notch of flaps. The flight instructor observed the airplane was then in a steep nose up stalling pitch attitude. He radioed instructions to "pitch down, pitch down", and with the airplane very low to the ground and drifting left, the student pilot radioed back asking the flight instructor to "say again". Control was lost and the airplane impacted a hangar about 650 feet to the left of runway center line. The impact resulted in substantial damage to the fuselage, empennage, tail surfaces, and both wings which were completely separated as the airplane penetrated the hangar wall. The fuselage came to rest inside the closed hangar and there was no postimpact fire. The student pilot reported that had attempted the go-around with too much pitch, too little speed, and not enough rudder input. He also reported that the accident would not have happened if he had spent more of his attention "flying the plane" and less attention communicating on the radio during a critical phase of flight.
Trimmed For Landing...And Then
When you throttle up for a go-around, you have aerodynamics working against you. On final approach, you're trimmed for landing speed, which is almost always slower than Vy (or Vx for that matter).
When you add full power and your airplane starts accelerating, it starts pitching up too.
When you look at final approach speeds vs. climb speeds, they're quite a bit different. Take the Cessna 172S, for example. Final approach speed is 61 knots, and Vy is 74 knots. So if you're trimmed for final approach and you add full power, your plane will start pitching up, trying to maintain that 61 knots you were trimmed for.
The danger, obviously, is when you let things continue to develop. If you're distracted and you forget to pitch down and re-trim the plane, you can over-pitch and get dangerously close to a stall.
Retracting Flaps Causes A Pitch Change
When you're on final approach, regardless of your plane, you typically have full or nearly full flaps in. And when you go-around, you retract flaps as part of your go-around procedure.
The problem is with flap retraction. When your flaps retract, your wing's center of lift moves forward, causing your plane to naturally pitch up.
At the same time, retracting flaps increases stall speed. When you combine a shifting center of lift and increased stall speed, it creates a recipe that can get you close to stall, if you don't correct by maintaining your pitch or pitching down.
Multiple Factors Working Against You
When you go-around, there are several factors working against you. You're trimmed for a speed slower than Vy, retracting flaps causes your plane to pitch up, and there are often times distractions inside and outside the cockpit.
When you combine all three, it creates a situation that could get you close to a power-on stall before you even realize what's happened.
This is not an original article. It first appeared on boldmethod.com on 13 April 2017. To read the original article click here.
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